Noninvasive psychophysical and electrophysiological techniques will be further developed and applied to the study of the function of the outer retina and choroid. Abnormalities of human cone photopigment kinetics will be studied using color matching techniques. Since color-matches depend on the concentration of photopigment, and maintenance of photopigment concentration requires the retinal pigment epithelium, the photoreceptors: and communication between them, color matching provides a sensitive probe of outer retinal function. Diseases to be studied (including diabetes, Best's disease, central serous retinopathy, age related maculopathy, retinal detachments, as well as others) have been chosen on the basis of their known affect on the eye. Comparison of results across diseases will allow us to test general features of retinal dysfunction. Color matching will also be used to study variations of extinction spectra and optical densitv in the population. At high retinal illuminances (when photopigment concentrations are low), color matches depend on the extinction spectra of the photopigments (and slightly on pre-retinal filters). At low retinal illuminances (when photopigment concentrations are high), color matches depend on both extinction spectra and optical density. By measuring in both conditions we can obtain sensitive measures of individual differences. Understanding individual differences may provide a better understanding of the determinants of visual sensitivity as well as provide an important basis for comparison to patient results. We will also develop a noninvasive test of photoreceptor transduction and adaptation based on the electrical use of the eye to steadily flickering lights (the steady-state electroretinogram or SSERG). Using rapidly flickering light allows isolation of photoreceptor responses, and studying the illiminance and modulation dependence of these responses allows us to indirectly measure very early events in the process of vision. Comparison of SSERG measurements to measurements using psychophysical techniques in the same patients allows us to better understand the pathophysiology of diseases affecting the outer retina.